Automatic sewing machine system



Dec. 19, 1967 c. J. BRYAN 3,358,626

AUTOMATIC SEWING MACHINE SYSTEM Filed Oct. 2 Sheets-Sheet l INVENTORCARNEY J BRYAN Dec. 19, 1967 c. J. BRYAN 3,358,626

AUTOMATIC SEWING MACHINE SYSTEM Filed Oct. 23, 1965 2 Sheets-Sheet 2INVENTOR CARNEY J BRYAN RNEYS United States Patent 3,358,626 AUTOMATICSEWING MACHINE SYSTEM Carney J. Bryan, Greensboro, N.C., assignor, bymesne assignments, to Ivanhoe Research Corporation, New York, N.Y., acorporation of Delaware Filed Get. 23, 1965, Ser. No. 502,970 8 Claims.(Cl. 112-2) The present invention relates to a fully automatic sewingmachine for stitching fabric work material along any desiredpredetermined path extending in more than one dimension and having asystem for sensing the correct positioning of fabric work material atall times during a complete operating cycle. More particularly, thesensing apparatus continuously detects the proper positioning of thework material in more than one coordinate direction throughout the fullcycle to assure that the desired stitching pattern is produced and thatthe completed work material is properly delivered.

This invention is an improvement in the automatic high-speed stitchingmethods and apparatus disclosed and claimed in application Ser. No.436,763, filed on Mar. 3, 1965, and which is assigned to the sameassignce as the present invention.

In an automatic sewing machine embodying the system of the presentinvention the various pieces of the fabric work material are supportedupon an electrically conductive work supporting surface upon which theycan readily be slid. They are propelled past the stitching station by aclamp member moving in more than one coordinate direction for producingthe desired multi-dimensional stitching pattern in the material. Thisclamp member engages the upper surface of the fabric material by afriction grip which exceeds the friction force between the lower surfaceof the material and the conductive surface, which is provided by aconductive table top. Thus, during the movement in two coordinatedirections the fabric material is driven by the differential in frictionexisting between the clamp member and the material on one hand and thatbetween the material and table top on the other hand.

There are periods during an operating cycle when the clamp member is incontinuous motion in two coordinates and the fabric work material as a.whole is intended accurately to follow this two-coordinate movementthroughout a complete cycle of operation. The table has an electricallyconductive top surface and electrically conductive sensing means aremounted upon the movable clamp and are resiliently biased down towardthe conductive table top. If at any time during an operating cycle thenon-conductive work material should accidentally become displacedrelative to the clamp member, then electrical contact is established toproduce an automatic protective sequence.

It is among the objects of the present invention to provide an automaticsewing machine system which sews the fabric work material along anydesired predetermined path in two coordinate directions at high speedwhile assuring proper positioning of the material during operation.

Advantageously, the present invention enables the stitching operation tostart at the edge or at any interior point in an expanse of workmaterial, and the stitching automatically progresses at a high rate ofspeed along straight lines and around bends and abrupt changes indirection to produce the desired path of stitches extending in twocoordinates in a manner suitable for automatically fabricating parts andcomponents of garments and the like in an automation system.

As used herein the term work material is intended to mean fabric, cloth,felt, canvas, leather, sheet or similar fabric-like goods upon which thestitching work is "ice performed. This term is intended to include allsuch types of goods able to accommodate small amounts of distortion inthe plane of the goods themselves, regardless of whether the material ofthe goods is in one piece or multiple pieces, one layer or multiplelayers, regardless of whether the goods are woven, non-woven, felted, insheet form, porous, perforate or imperforate, natural or synthetic orblended.

The term stitching along a path extending in two dimensions (in twocoordinates) is intended to mean that the path of the stitches in thework material can be defined with respect to the general plane of thework material in terms of two coordinates, and regardless of whether thework material itself as a whole is planar or non-planar or issubsequently used in a planar or non-planar form. In other words thestitching path may include straight-line segments, curved segments,angles, abrupt changes in directions, spirals, cusps, and the like.

In this specification and in the accompanying drawings, is described andshown an automatic sewing machine system embodying the presentinvention, but it is to be understood that this disclosure is notintended to be exhaustive nor limiting of the invention, but on thecontrary is given for purposes of illustration in order that othersskilled in the art may fully understand the invention and the manner ofapplying the system in practical use and will understand how to modifyand adapt it in various forms, each as may be best suited to theconditions of a particular application.

The various objects, aspects, and advantages of this invention will bemore fully understood from a consideration of the followingspecification in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of an automatic highspeed two-coordinatesewing machine system embodying the present invention;

FIGURE 2 is a top plan view of the movable work clamp member includingthe sensing contact elements mounted thereon, and shown on a largerscale than FIG- URE 1;

FIGURE 3 is a partial sectional view taken along the line 33 of FIGURE 2and shown on enlarged scale;

FIGURE 4 is a partial sectional view taken along the line 44 of FIGURE 2and showing operation in relationship with the needle; and

FIGURE 5 is a schematic electrical circuit diagram of the controlcircuit.

In FIGURE 1, is shown an automatic sewing machine system 10, and thework material W which is being stitched is a plurality of layers offabric to be used in part of a garment. This work W is held by a rapidlymovable clamp member 12 which frictionally engages the top surface ofthe work and serves to slide the work in two coordinate directions overa work table 14. Thus, the work is moved past a reciprocating needle 16secured in the needle bar 17 of a high-speed sewing machine 18, and thissystem is capable of producing a line of stitches S along any desiredstitching path extending in two coordinate directions.

As shown in FIGURES 2, 3 and 4, the clamp member 12 includes alightweight rigid frame 20 with a resilient coupling medium 22 attachedto the frame and pressing down onto the work W closely adjacent to theline of stitches S. The resilient coupling medium 22 is compliant incompression so as to accommodate different thicknesses in the workmaterial, for example where different numbers of layers are present atdifferent regions of the work. This coupling medium 22 is also compliantin shear to accommodate the arresting of small localized areas of thework W during each instant the needle 16 is inserted in the work whilethe remainder of the work is in continuous movement at high speed. Inthis example the coupling medium 22 is sponge rubber.

This automatic sewing machine system is capable of stitching the workmaterial W at a high rate of speed, except that the sewing machine 18 isrun at a slower rate for brief instants at the very beginning and at theend of each stitching pattern S. The clamp member 12 is connected to anarm 24 which is driven by drive mechanism generally indicated at 25, aswill be described in detail further below.

When the stitching pattern S has been completed, the needle 16 is raisedup out of the way and the thread is automatically cut as explained insaid copending application Ser. No. 436,763. Then the clamp member 12 isquickly moved to the desired delivery point on the work table 14 and iselevated so as to disengage the resilient coupling medium 22 from thework to release the completed work at that delivery point. While theclamp member 12 is elevated, it is brought into relative position abovea new piece of work material at a work receiving point. The clamp memberis lowered onto this new work and is quickly moved back into operativerelationship with respect to the needle 16. It is noted that thecompleted work may be delivered to a different point on the work table14 from that at which the new work is received, or the delivery andreceiving locations may be the same, as may be desired in a particularproduction application.

During the stitching operation the work material W is being slid overthe table 14 past the needle 16 which is reciprocated up and down by theneedle bar 17. The needle point passes down through a throat opening 26in the table 14, and the stitches are formed between a top thread 27carried by an eye in the needle and a lower thread (not shown) suppliedfrom a bobbin mechanism below the table in conventional manner. Thelocalized region of the work material which is briefly penetrated by theneedle 16 is arrested in its movement by an annular arrestor foot 28surrounding the needle. This arrester moves up and down into contactwith Work material W in timed relationship with the needle stroke asexplained in said copending application. In certain productioninstallations the arrester foot 28 may be omitted, and the needle 16itself serves to arrest the forward movement of that region of the workmaterial being penetrated by the needle.

The work material W as, a Whole is driven by the differential infriction between the coupling medium 22 and the top surface of the workW on one hand and that between the lower surface of the work and thetable 14.

this table top 14 is formed of polished aluminum or stainless steel. Itis electrically connected as indicated at 29 to the main chassis 30(FIG. 1) of the system so that the table top 14 is always held at groundpotential. Electrically conductive sensing means 32 are carried by themovable clamp 12 and are positioned to rest upon the very edge region ofthe work material being stitched. Upon any slight displacement of thework material W relative to the clamp member 12, the sensing means 32touches the table 14 to complete an electrical circuit, actuating aprotective sequence, as will be explained further below. In thisillustrative embodiment the sensing means 32 includes a plurality ofsensing contact elements mounted upon the clamp frame 20 and insulatedtherefrom by insulating bushings 34 and spacers 36. Each sensing element32 has an L-shape including a terminal portion 37 resting upon thespacer 36 and secured by a mounting screw 38 to the bushing 34, which isheld in an undercut socket in the frame 20. An intermediate springportion 39 urges a vertical leg 40 down toward the conductive table top14. The. lower end of the leg 40 is bent up to form a rounded contact 41which avoids snagging the work W.

As shown in FIGURE 2, there are sensing openings 42 which are positionedimmediately adjacent to spaced points along a plurality of the difierentedges 44, 45, 46 and 47 of the work material W. The vertical legs 40extend down through these openings 42 so that the contacts 41 rest uponthe very edge region of the material adjacent to these edges 44-47. Itis to be noted that the respective edges 44-47 face in substantiallydifferent directions, so that any slight displacement of the workmaterial W in any direction relative to the clamp member 20 will permitone or more of the non-snagging contacts 41 to slide ofi of therespective edge and to spring down against the table 14. This completesa control circuit as will be explained in connection with FIG- URE 5 soas to stop the system.

In the illustrative example the stitching pattern S extends alongadjacent to the edge 46, and in order to assure that this edge 46remains properly positioned, the clamp frame 20 has a branch 48extending along beside the edge 46 and connected by a back portion 49 tothe main body of the clamp frame 20. Two of these contacts 32 aremounted on this branch 48 so that they can engage the edge region 46while providing clearance for the line of stitches S, as seen in FIGURE4. The stitching path progresses along an open channel 50 between thebranch 48 and the main body of the clamp frame 20, and the resilientcoupling medium 22 presses down against the work W near to the intendedline of stitches.

The terminals 37 are connected by insulated leads 52 to a control wire54 which is mounted on the arm 24 extending along the arm past a fixedpivot point 56 in the drive mechanism 25 and connected into a controlcircuit 58.

As shown in FIGURE 1 the arm 24 is driven by a pair of lightweighttriangular cam follower levers 64 and 65 driven by a pair of cams 66 and67 mounted on a common vertical shaft 70. The levers 64 and 65 aredisposed on generally opposite sides of the cams 66 and 67 and arearranged and connected so that the lever 64 produces mainly movement ofthe arm 24 in a direction parallel to its own length while the otherlever 65 mainly produces angular movement of the arm 24 about a pivot71. The lever 64 has the fixed pivot 56 and a follower roller 73, sothat it produces velocity multiplication at the pivot connection 71 withthe arm. Consequently, the arm 42 is moved in a direction along itslength at a higher rate of speed than that imparted by the cam 66 to theroller 73.

The other lever 65 has a cam follower roller 74, a pivot connection 75to a cross link 76, and an intermediate fixed pivot 77. Thus, it hasapproximately equal lever arms to provide a velocity at the pivotconnection 75 which is approximately equal to that imparted by the cam67 to the roller 74. This velocity is transferred by the cross link 76to a pivot connection 78 on the arm 24. With this arrangement there is amovement of the end of the arm 24 perpendicular to its length which isat a higher rate of speed than that imparted by the cam 67 to the roller74. Advantageously, this arrangement produces velocity multiplicationwith respect to both coordinates of motion that are substantially equal.Consequently, the cams 66 and 67 may be of substantially the sameover-all size for a wide variety of stitching patterns, thus minimizingthe over-all sizes and masses of the levers, link 76 and arm 24 whileenabling large pattern areas to be sewn at high speed.

The arm 24 is hollow and is tapered down toward both ends and has amaximum width near the pivot connection 78 to resist bending stresswhere the lateral thrusts are imparted. The triangular levers 64 and 65are hollow, and the cross link 76 is tubular to provide maximum rigidityto mass ratio.

In order to hold the follower rollers 73 and 74 against their respectivecams, spring forces of substantially constant magnitude and directedinwardly generally toward the shaft 70 are applied to each lever at apoint adjacent to the follower roller. For example, in this apparatusshown these forces are provided by strip springs 80 and 81 of the typewhich are self-winding on drums to generate a generally constant tensionforce regardless of extension, available commercially.

To prevent the cam movement from being influenced by the forces of thefollower rollers 73 and 74 bearing against them and thus reactingagainst back lash in the drive gearing, suitable braking means areprovided. For example, there is a large diameter disk caliper brake 82providing a constant drag force upon a disc 83 on the shaft 70 so thatany back lash present is always taken up in the same direction withrespect to the rotation of the shaft 70.

To provide downward force on the clamp member 12 with a minimum of masseffect on the arm 24 there is a strip spring 84, which is similar to thesprings 80 and 81 discussed previously. This tension spring 84 issecured to a long, substantially vertical cable which is connected tothe underside of the arm 24 so as to pull downwardly on this arm withrelatively constant force regardless of the horizontal position of thearm.

When the stitching of the pattern is completed, then the clamp member 12is moved to a predetermined delivery position at which the arm 24 israised against the force of the spring 84, thus releasing the completedwork from engagement with the resilient compliant means 22. For raisingthe arm 24, lift means 85 are provided which engage the arm in thedelivery position. After the completed work has been removed a new pieceof work can be placed beneath the clamp member 12 or, alternatively, theclamp may be moved to another position at which it can be raised byanother lift mechanism similar to the lift means 85.

The driving power for the system is provided by a main drive motor 90connected to a counter shaft 91, and a main shaft 92 parallels thiscounter shaft. The main shaft 92 can be driven from the shaft 91 througha highspeed clutch 93 and a timing belt 94. This is a magnetic clutch93, and when it is actuated the sewing machine 18 sews at a high rate ofspeed. For operation at an intermediate speed if desired, a timing belt95 is connected to an intermediate speed magnetic clutch 96. Forproviding a slow operating speed, both of the clutches 93 and 96 aredisengaged, and the driving power is supplied from a drive motor andspeed reducer 97 through a slowspeed clutch 98.

The rotation of the main shaft 92 bears a known speed relationship withrespect to the rotation of the cam shaft 70, the drive path extendingthrough a coupling 99, a speed-reduction gear mechanism 100, and achange gear train 101, 102 to a driven gear 103 on the shaft 70. Tochange the speed relationship between the rotation of the main shaft 92and the cam shaft 70, the gears in the train 102 are changed.

The cams 66 and 67 are individually removably secured to the shaft 70 ata fixed angular orientation. To change the sewing pattern for stitchingdifierent pieces of work material, these cams are replaced by othercams. Also, the clamp member 12 is removed from the arm 24 bydisconnecting bolts 104 and is replaced by a different clamp memberhaving a shape corresponding with the desired stitching pattern. Thecontrol wire 54 includes a disconnect plug 106 for attaching the leads52 from the sensing elements on the clamp member.

In order to drive the sewing machine 18 at a known relationship withrespect to the cam shaft 70, a drive path is provided from the mainshaft 92 to a driven sheave 108 on the crank shaft 109 of the sewingmachine. This drive path including a timing belt 110, a drive disengageand needle raise and lock-up mechanism 112 and a timing belt 113.

As shown in FIGURE 5, the control wire 54 is connected to a relaywinding 114 to be energized by the lowvoltage secondary 116 of astep-down transformer 117 having its primary 118 connected across thealternating current supply lines 119 and 120, which supply A.C. atsuitable voltage, for example 120 volts, 60 cycles. If the work Wbecomes displaced, then one or more of the contacts 41 touches the table14 to complete a circuit through the secondary 116 back to the groundconnection 29, thus energizing the relay winding 114 to opennormally-closed relay contacts 122 and to close normally-open relaycontacts 123. Closure of the contacts 123 completes a circuit from theline 119 through a lead 124, through contacts 123, to an alarm signal125 and through a lead 126 to an electromagnetic brake 127 (see alsoFIGURE 1), which immediately stops the main shaft 92. The operator isalerted by the alarm 125 and can reposition or remove the work W bylifting the arm 24 against the force of the spring 84.

During normal operation the contacts 123 are open, and the brake 127 isoperated by a circuit extending from the line 119 through a lead 128 andthrough control means 130 connected to the brake 127. Also, duringnormal operation the contacts 122 are closed, and the respectiveclutches 93, 96 and 98 are operated by control means 131, 132 and 133.These control means 130-133 include switches and relays which areactuated in accordance with the position of the cams 66 and 67 toproduce the desired cycle of operation of the sewing machine 18.

It will be appreciated that this automatic system is intended to handlework materials having non-conductive or high insulating characteristicsso as to maintain the relay winding 114 deenergized so long as all ofthe contacts 41 are resting upon the work W. If the work material Wincludes any conductive filaments or layers, such as wire strands orwire gauze, then it is still possible to utilize this system providedthat the work material has a sandwich construction such that one or morelayers is of insulating material. The criteria to observe are that thecontacts 41 remain insulated from the table 14 when they rest on thework W. To prevent inadvertent actuation of the system in the case ofwork material containing conductive filaments or layers, it may bedesirable to insulate the needle from the common return circuit. Thereason for insulating the needle in such a case is that upon penetrationof the work it may touch the conductive strands or layers which may alsobe touching one of the contacts 41.

From the foregoing it will be understood that the automatic sewingmachine system of the present invention is well suited to provideseveral advantages in operation. It will be appreciated from thisdescription that various possible embodiments may be made of the variousfeatures of this invention and the apparatus herein described may bevaried in different parts, all without departing from the scope of theinvention, and that all matter hereinbefore set forth or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense, and that, in certain instances, some of the features ofthe invention may be used without a corresponding use of other features,all without departing from the scope of the invention as defined by thefollowing claims.

What is claimed is:

1. A sewing machine system for automatically sewing fabric Work materialalong a stitching path extending in two dimensions comprising a sewingmachine having needle means operating at a stitching station, a worktable surrounding said stitching station and having an electricallyconductive top surface upon which the work material is slidable, amovable clamp member engageable down upon the fabric work material,drive means for moving said clamp member, control means for said drivemeans, electrical contact sensing means extending down from said clampmember positioned to rest upon the edge regions of fabric work materialproperly positioned beneath the clamp member, and circuit meansinterconnecting said contact sensing means, said control means and saidconductive top surface for stopping said drive means if the fabricworkpiece shifts its position with respect to the clamp member to permitsaid sensing means to touch said conductive top surface.

2. An automatic sewing machine system comprising a. sewing machineincluding needle means for stitching fabric workpieces, a work tablehaving a smooth top surface for supporting the fabric workpieces, saidtop surface being electrically conductive and providing low friction forfabric workpieces being slid thereover, automatic drive means, movablearm means driven by said drive means, said arm means having a clampmeans providing high friction for gripping and sliding the workpiecesover said table surface relative to said needle means to stitch theworkpiece, a plurality of sensing contacts mounted on said clamp meansand being resiliently biased toward said conductive table surface, saidsensing contacts being normally insulated from said conductive topsurface by a fabric workpiece properly positioned beneath said clampmeans, control means for controlling said drive means, and circuit meansinterconnecting said control means and said conductive table surface andsaid sensing contacts.

3. A sewing machine system for automatically sewing fabric work materialalong a stitching path extending in two dimensions comprising a sewingmachine having needle means operating at a stitching station, a worktable surrounding said stitching station and having an electricallyconductive top surface upon which the work material is slidable, amovable arm, a clamp member carried by said arm and engageable down uponthe fabric work material, drive means for moving said arm, control meansfor said drive means, said control means being connected to said tabletop, electrical contact sensing means extending down from said clampmember in positions to rest upon the edge regions of fabric workmaterial properly positioned beneath the clamp member, and an electricalcircuit extending from said control means along said arm to said contactsensing means for stopping said drive means if the fabric workpieceshifts its position with respect to the clamp member to perirnt saidcontact sensing means to touch said conductive top surface.

4. An automatic sewing machine system comprising a sewing machineincluding needle means for stitching fabric workpieces, a work tablehaving a smooth top surface for supporting the fabric workpieces andupon which the workpieces are slidable, said top surface beingelectrically conductive, automatic drive means, movable arm means drivenby said drive means, said arm means having a clamp frame, a resilientcoupling medium secured to the bottom of said clamp frame providing highfriction for gripping and sliding the workpieces over said table surfacerelative to said needle means to stitch the workpiece, a plurality ofsensing elements mounted on said clamp frame and being insulatedtherefrom, said sensing elements having rounded contact ends extendingdown below said resilient coupling medium and being resiliently biasedtoward said conductive table surface, said contact ends being normallyinsulated from said conductive top surface by a fabric workpieceproperly positioned beneath said resilient coupling medium, controlmeans for controlling said drive means, and circuit meansinterconnecting said control means and said conductive table surface andsaid sensing elements.

5. A sewing machine system for automatically'sewing fabric work materialalong a stitching path extending in two dimensions comprising a sewingmachine having needle means operating at a stitching station, a worktable surrounding said stitching station and having an electricallyconductive top surface upon which'the work material is slidable, amovable clamp member having a resilient medium secured thereto andproviding a firm frictional grip upon the fabric work material when saidresilient medium is engaged down upon the Work material,

drive means for moving said clamp member, control means for said drivemeans, said clamp member having an open channel therein along which anedge of the work material is stitched, a sensing element mounted uponsaid clamp member and having a contact extending down in a position toengage the work material immediately adjacent to said edge when the workmaterial is properly positioned beneath said resilient medium, saidcontact being resiliently urged down toward the edge of the workmaterial, and electrical circuit means interconnecting said contact,said control means and said conductive table surface for stopping saiddrive means if the fabric workpiece shifts its position with respect tothe clamp member to permit said contact to touch said conductive topsurface.

6. A sewing machine sysem for stitching fabric work material along astitching pattern extending in more than one dimension comprising needlemeans operating at a stitching station, an electrically conductive worksupporting surface adjacent to said stitching station, said conductivesurface enabling the work material to be slid thereon, movable clampmeans engageable with the work material for holding the work materialagainst said surface, drive means for moving said clamp means in morethan one direction relative to said stitching station for moving thework material to produce the stitching pattern, electrical contact meansmounted on said clamp means and springbiased toward said conductivesurface, said contact means being positioned to engage an edge region ofthe work material when the work material is properly positioned withrespect to said clamp means, and control circuit means interconnectingsaid contact means with said drive means and said conductive surface.

7. A sewing machine system as claimed in claim 6 and wherein saidcontact means are positioned to engage the edge region of the workmaterial at a plurality of locations spaced about the perimeter of thework material.

8. A sewing machine system as claimed in claim 6 and wherein said clampmeans has a first portion and a branch portion extending along besidesaid first portion providing a stitching channel through which saidneedle means can stitch the work material along a path extending betweensaid branch portion and said first portion, and said contact meansincludes a contact element mounted upon said branch portion, springbiased toward said conductive surface and positioned to engage an edgeregion of the work material immediately adjacent to said stitchingchannel and said contact means includes another contact element mountedupon said first portion, spring biased toward said conductive surfaceand positioned to engage an edge region of the work material remote fromsaid channel.

References Cited UNITED STATES PATENTS 2,290,123 7/ 1942 Wilfong.

2,483,138 9/1949 Helmer 1l22l9 2,845,885 8/1958 Scarrone ll2203 X3,013,513 12/1961 Judleson 112203 3,072,081 l/1963 Milligan et al 1l223,170,423 2/1965 Henebry 1122 3,204,590 9/1965 Rockerath et al. 1l2203 XPATRICK D. LAWSON, Primary Examiner.

J. R. BOLER, Assistant Examiner,

1. A SEWING MACHINE SYSTEM FOR AUTOMATICALLY SEWING FABRIC WORK MATERIALALONG A STITCHING PATH EXTENDING IN TWO DIMENSIONS COMPRISING A SEWINGMACHINE HAVING NEEDLE MEANS OPERATING AT A STITCHING STATION, A WORKTABLE SURROUNDING SAID STITCHING STATION AND HAVING AN ELECTRICALLYCONDUCTIVE TOP SURFACE UPON WHICH THE WORK MATERIAL IS SLIDABLE, AMOVABLE CLAMP MEMBER ENGAGEABLE DOWN UPON THE FABRIC WORK MATERIAL,DRIVE MEANS FOR MOVING SAID CLAMP MEMBER, CONTROL MEANS FOR SAID DRIVEMEANS, ELECTRICAL CONTACT SENSING MEANS EXTENDING DOWN FROM SAID CLAMPMEMBER POSITIONED TO REST UPON THE EDGE REGIONS OF FABRIC WORK MATERIALPROPERLY POSITIONED BENEATH THE CLAMP MEMBER, AND CIRCUIT MEANSINTERCONNECTING SAID CONTACT SENSING MEANS, SAID CONTROL MEANS AND SAIDCONDUCTIVE TOP SURFACE FOR STOPPING SAID DRIVE MEANS IF THE FABRICWORKPIECE SHIFTS ITS POSITION WITH RESPECT TO THE CLAMP MEMBER TO PERMITSAID SENSING MEANS TO TOUCH SAID CONDUCTIVE TOP SURFACE.